A new study indicates that the megadrought that struck the Amazon in 2010 devastated millions of hectares of rainforest, shedding a new light over the debate over the effects of recent climatic events.

The initial findings were presented at the fall meeting of the American Geophysical Union. They indicate that as many as one in twenty-five trees died in areas with the most severe water scarcity. The findings also suggest that previous techniques using satellites to measure drought stress in rainforests may be missing impacts of a warming global climate, which is believed will cause more droughts in these critical habitats.

The Carnegie Airbone Observatory, which scans forests from a slow-flying plane 2,000 meters above treetops, measured the shape and chemical signatures of the forests using lidar and a spectrometer. This allowed scientists to identify individual tree species, determining their health and measuring their size and mass precisely from the air. The 2010 drought followed a similarly sever one in 2005 and a less intense one in 2007.

More than a year and a half before the drought began, scientists flew repeated missions over a 500,000-hectare patch of forest in Brazil and Peru. Rainfall data indicated that roughly three-fifths of that area had gone through a severe drought. Previous studies indicated that rainforests could be more resilient to climate change than ecosystem models assume, but this analysis of the new data shows that repeated droughts are harming the rainforests.